Fuel cells are used or have been proposed as a power source in many applications, such as in electrical vehicular power plants to replace internal combustion engines and in stationary applications to produce electrical power. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied to the anode of the fuel cell and oxygen is supplied to the cathode. PEM fuel cells include a membrane electrode assembly (MEA) comprising a thin, proton transmissive, non-electrically conductive solid polymer electrolyte membrane having the anode catalyst on one of its faces and the cathode catalyst on the opposite face. The MEA is sandwiched between a pair of electrically conductive elements which serve as current collectors for the anode and cathode, and contain appropriate channels and/or openings therein for distributing the fuel cells' gaseous reactants over the surfaces of the respective anode and cathode catalysts. A typical PEM fuel cell and its MEA are described in U.S. Pat. Nos. 5,272,017 and 5,316,871 issued respectively Dec. 21, 1993 and May 31, 1994 and assigned to General Motors Corporation.
The term “fuel cell” is typically used to refer to either a single cell or a plurality of cells depending on the context. A plurality of individual cells are commonly bundled together to form a fuel cell stack. Each cell within the fuel cell stack comprises the MEA described earlier, and each MEA provides its increment of voltage.
During the operation of the fuel cell stack, heat is generated that needs to be removed. To remove the heat, the fuel cell stack includes a coolant flow path that allows a coolant flow to pass through the fuel cell stack and extract heat therefrom. During the flow of coolant through the fuel cell stack, however, gas, such as air, can become entrapped within the coolant flow path in the fuel cell stack. The entrapped gas may prevent the coolant from flowing through the entire coolant flow path and possibly cause some components to overheat or operate at an undesirable elevated temperature. Accordingly, it would be desirable to remove gas from the coolant flow path. Furthermore, it would be advantageous if the removal of gas from coolant flow path is achieved with a minimal addition or change to the fuel cell stack.